1. Field of the Invention
This invention relates to a picture signal processing method and apparatus in which video source signals, that is interlaced video signals conforming to, for example, NTSC standard television broadcasting system, obtained on conversion (so-called tele-cine conversion) from a 24-picture frame-per-second picture from a film source, such as a motion picture, are re-converted for generating the signals corresponding to a pre-tele-cine-conversion picture, that is picture signals of 24 picture frames per second directly obtained from the film source.
2. Description of the Related Art
For converting a 24-picture frame-per-second picture, obtained from a film source, such as a motion picture, into a 30-frame-per-second interlaced video signals of, for example, the NTSC system, as one of the standard television broadcasting systems, by so-called tele-cine conversion, the frame number conversion, more specifically, the field number conversion, is performed for matching two picture frames of the film to 2.5 frames or five fields of the NTSC system, because the rate of pictures obtained from the film source is 24 picture frames per second, whereas that of pictures of the NTSC system is 30 frames per second, more precisely, 29.97 frames per second, or 60 fields per second.
As a technique for such tele-cine conversion, a so-called 2-3 pull-down method, is widely employed.
If the respective picture frames of a film are denoted by picture frame numbers of 1, 2, 3, . . . , first and second fields making up a frame of the NTSC interlaced video signals are denoted as f1 and f2 and pictures represented as the field f1 or the field f2 are associated with the picture frame numbers, picture signals of the two fields of the first and second field f1 and f2 making up a sole frame of the interlaced video signals are generated in the 2-3 pull down from a picture of the picture frame number 1, picture signals of the next three fields are generated from a picture of the picture frame number 2 and picture signals of the next two fields are generated from a picture of the picture frame number 3, as shown in FIG. 1. This sequence of operations is performed repeatedly. In an example shown in FIG. 1, a one-frame picture in the NTSC system is split into a top half T and a bottom half B and respective pictures in these half portions are indicated in association with the picture frame numbers. In FIG. 1, b.sub.f and b.sub.F denote a boundary between the first field f1 and the second field f2 in one frame and a boundary between frames, respectively.
For re-converting video-source signals, that is interlaced video signals of the NTSC system, obtained by the above-described tele-cine conversion, for regenerating signals corresponding to pre-tele-cine conversion pictures, that is the same 24-picture frame-per-second picture signal as those directly obtained from the film source, the conversion operation as shown for example in FIG. 2 is performed. The manner of representation in FIG. 2 is similar to that in FIG. 1. Such regeneration of the same picture signals as those from the original film source from the video source signals obtained on tele-cine conversion is termed hereinafter as the reverse tele-cine conversion.
In the reverse tele-cine conversion, the fields having overlapped contents are detected and deleted from the video-source picture signals and the 24-picture frame-per-second picture signals are generated from the remaining picture signals, as shown in FIG. 2. Meanwhile, the fields to be deleted in the above example are third fields, for example, in case the picture from the same picture frame of the film occurs three successive fields.
If tele-cine conversion is performed so that the picture frame boundary in the film source is coincident with the frame or field boundary in the video source, as shown in FIG. 1, reverse tele-cine conversion becomes easily feasible by a method shown in FIG. 2.
However, depending on the sorts of the tele-cine conversion devices employed, conversion may be performed such that the picture frame boundary in the film source is not coincident with the frame or field boundary in the video source of, for example, the NTSC system, with the picture displayed in the top half T being different from that displayed in the bottom half B, that is with the pictures from different picture frames being displayed in these top and bottom half portions. This results from the fact that, although the film playback time and the time of the video signal produced on tele-cine conversion are synchronized with each other, there is a lack of phase control between the picture frames and the fields, that is that the picture frame breaking points are not controlled to be coincident with the field boundaries. In addition, the phase difference between the picture frames and the fields, that is a time period in which the picture frame breaking points coincide with the field boundaries, is not constant and depends upon the tele-cine conversion devices employed.
Thus, if the NTSC system video source, obtained by the tele-cine conversion device, is reverse tele-cine converted by the technique described above, pictures of picture frames previous or subsequent to a picture frame marked with an asterisk *, obtained on reverse tele-cine conversion, exist in the picture of the picture frame, as shown in FIG. 4 similar in the manner of representation to FIG. 2, such that a satisfactory picture cannot be obtained. For example, a field f1 of a frame indicated by a frame number F2 in the video source of the NTSC system shown in FIG. 4 is composed of the top half portion T and the bottom half portion B derived from different picture frames, that is the picture frames of the picture frame numbers 1 and 2, such that the picture obtained on reverse tele-cine conversion of the picture signals having the frame number F2 are deteriorated in picture quality.
In addition, with the above technique for reverse tele-cine conversion, it is difficult to detect the fields to be deleted from the video source shown in FIG. 3.